U.S. Pat. No. 6,483,322 (corresponding to JP-A-2000-40047) discloses a capacitive acceleration sensor used in an automotive vehicle. In a sensor element of the sensor, a capacitive variation is generated by an acceleration variation. The capacitive variation is converted into an electrical signal by a capacitance-voltage (C-V) conversion circuit. The converted signal is differentially amplified by a signal processing circuit including a sampling and holding circuit and a switched capacitor circuit. Thus, the sensor can output an output signal corresponding to the acceleration variation.
In order to output a sensitive output signal, a high-power C-V conversion circuit and a high-gain amplifying circuit are required in the capacitive acceleration sensor. Therefore, the C-V conversion circuit includes a switched capacitor system, and performs a high-power C-V conversion.
In the C-V conversion circuit including the switched capacitor system, an analog switch has a circuitry shown in FIG. 5. That is, the analog switch includes a P-channel metal-oxide semiconductor (Pch-MOS) transistor 101 and a N-channel metal-oxide semiconductor (Nch-MOS) transistor 102. The Pch-MOS transistor 101 has a back gate potential VG of Vdd, and the Nch-MOS transistor 102 has a ground potential GND as its back gate potential VG. Then, a potential difference is generated between an input potential from a sensor element and the back gate potential VG of the transistor 101, 102. Therefore, electricity leak may be generated in a semiconductor substrate, on which the transistors 101, 102 are formed. Especially, the electricity leak may be large in a high-temperature range. Thus, a temperature characteristic of a zero-point offset or sensitivity may be lowered, especially in the high-temperature range.